fix flow-bin verification on Windows

Author: mroch

lib/flowLSP/utils/getVerifiedFlowBinPath.js

@@ -22,7 +22,7 @@ function getFlowBinDirPrefixForPlatform(): null | string {
             null;
 }
 
-async function getFlowBinRelativePath(flowBinModulePath: string): Promise<string> {
+async function getFlowBinRelativePath(flowBinModulePath: string): Promise<{|flowBinDirName: string, flowBinName: string|}> {
     const dirPrefix = getFlowBinDirPrefixForPlatform();
     if (!dirPrefix) {
         throw new Error(`Failed to determine correct binary for platform ${process.platform} and arch ${process.arch}`);
@@ -38,7 +38,7 @@ async function getFlowBinRelativePath(flowBinModulePath: string): Promise<string
     if (!flowBinName) {
         throw new Error(`Failed to find flow binary in ${flowBinDir}`);
     }
-    return path.join(flowBinDirName, flowBinName);
+    return {flowBinDirName, flowBinName};
 }
 
 async function getShasums(flowBinModulePath: string, logger: Logger): Promise<Buffer> {
@@ -59,7 +59,8 @@ async function getShasums(flowBinModulePath: string, logger: Logger): Promise<Bu
     }
 }
 
-function getShasum(shasums: string, flowBinRelativePath: string): string {
+function getShasum(shasums: string, flowBinDirName: string, flowBinName: string): string {
+    const flowBinRelativePath = `${flowBinDirName}/${flowBinName}`;
     const shasum_lines = shasums.split(/\r?\n/);
     const shasum_line = shasum_lines.find(line => line.includes(flowBinRelativePath));
     if (!shasum_line) {
@@ -74,8 +75,8 @@ export default async function(flowBinModulePath: string, logger: Logger): Promis
         const shasums = await getShasums(flowBinModulePath, logger);
 
         // successfully verified SHASUM256.txt, now we can use it to verify the flow binary
-        const flowBinRelativePath = await getFlowBinRelativePath(flowBinModulePath);
-        const flowBinPath = path.join(flowBinModulePath, flowBinRelativePath);
+        const {flowBinDirName, flowBinName} = await getFlowBinRelativePath(flowBinModulePath);
+        const flowBinPath = path.join(flowBinModulePath, flowBinDirName, flowBinName);
         const hash = createHash('sha256');
         const flowBinReadStream = createReadStream(flowBinPath);
         const flowBinHashPromise = new Promise((resolve, reject) => {
@@ -84,7 +85,7 @@ export default async function(flowBinModulePath: string, logger: Logger): Promis
         });
         flowBinReadStream.pipe(hash);
         const flowBinHash = await flowBinHashPromise;
-        const shasum = getShasum(shasums.toString(), flowBinRelativePath);
+        const shasum = getShasum(shasums.toString(), flowBinDirName, flowBinName);
         if (flowBinHash !== shasum) {
             throw new Error(
                 `Hash of ${flowBinPath} does not match hash from SHASUM256.txt:\n` +